Traditional source of electric power are fossil fuels plants, hydro electric and nuclear power plants. These plants serve many remote consumers using power transmission network or Power Grid. For efficient transmission of the power generated at the generating stations to the consumers, the power grid uses Alternate Current (AC) technology. Private residences, industrial complexes, streets, public buildings and other facilities use the AC power. The AC power generated in different countries has different line voltages and line frequencies.
Alternate energy sources such as Solar Power, Fuel Cells and Wind Energy are being produced. The energy generated using alternate energy is typically Direct Current (DC). Large amounts of electrical energy cannot be stored economically. Small quantity of generated energy is stored in batteries. Either all of the generated electrical power is used or the power is generated when there is a demand for energy.
Electrical power can be produced on demand with fossil fuels and fuel cells. The power generated from the nature's sources such as solar energy and wind energy can only be generated when those sources are available. Excess electrical energy, that cannot be consumed at a particular location or stored in local batteries, is fed back to the traditional power grid. To be compatible with the traditional AC power grid and electric appliances, the DC electrical power generated from these alternate sources are converted to AC power.
A power converter or a power supply converts the Alternating Current (AC) electrical power at line voltage and frequency to Direct Current (DC) or AC to AC at different voltage levels and frequencies or DC to DC at different voltage levels used by electronic appliances and equipment. A power inverter converts DC at to AC voltages and frequencies.
The use of power supplies and inverters has increased, due to ubiquity of consumer and enterprise electronic products and increased reliance on alternate energy sources. U.S. Environmental Protection Agency, in their presentation “A Strategy to Improve the Efficiency of Power Supplies” estimate that there are more than 10 billion AC/DC power supplies used in computing, telecommunications and consumer electronics worldwide. The portable power supplies and battery chargers used for hand held electronic equipment are experiencing growth due to ubiquitous lap top personal computers, cellular telephones and other hand held electronic equipment. These electronic equipments use different voltage types such as AC or DC and at different voltage levels, frequencies and power conversion capacity. Different type of converters and or inverters may be in use at the same facility for different electronic appliances.
Inefficient incandescent bulbs are being used for lighting all over the world. International Energy Agency (IEA) claims that a switch over to efficient lighting systems could reduce global electrical demand by nearly 10 percent. To replace incandescent lamps, low voltage compact fluorescent lamps, florescent lamps, Light emitting diodes (LED), and other low voltage lighting products are being used in increasing numbers. The low voltage power for these lighting products is facilitated by power converters. Some of these converters are plugged into the wall sockets even when they are not is use. The converters consume power when they are idle, wasting energy. The energy wasted due to power converter inefficiencies increases as the number of the converters increase. High conversion efficiency, shutting off converters on Idle mode and Multimode operation to reduce the number of converters in a location contribute significantly for energy saving.
Electric Vehicles (EV) use electric power stored in DC batteries. The DC battery energy is converted to various DC and AC voltage levels to operate the Electric vehicle motors. AC Energy stored in the motor windings has to be converted back to DC voltages when the breaks are applied. Therefore, bidirectional inverters and converters are needed. The batteries operated by chemical reactions to store or charge and deliver power. So, batteries are limited by the slow chemical conversion time. Method of delivering power on demand while the Electric Vehicle is operating is needed. Fast charging method of batteries at home and public power fueling stations are also needed.
Linear Power Supplies (LPS) and or Switched Mode Power Supplies (SMPS) are used for power conversion and inversion. LPS convert the utility line voltage AC, at line frequencies, to required AC voltage levels at utility line frequencies using step up or step down transformers. The converted AC voltage is used for AC applications or it is rectified, transformed and regulated to the desired DC voltage level.
The utility AC line of different countries has different line voltages and line frequencies. A common LPS can be designed to address different voltages by the use of multiple windings on the transformer and selecting the winding for the specific voltages. U.S. Pat. No. 5,973,948 illustrates a mechanical switching method using two transformer windings for two different line voltage levels.
Transformers and magnetic inductors are two major components of the power conversion technology. Transformers are used to provide galvanic isolation and voltage conversion. Utility AC line frequencies are normally between fifty and sixty cycles per second or Hertz (Hz). Four hundred (400) Hz is power used in the aircraft. The physical size of magnetic components varies inversely with the frequency. As a result, the magnetic transformer in an LPS is large because it uses low line frequency directly. Most LPS use linear regulators, which are inefficient and need large heat sinks.
Switched Mode Power Supplies (SMPS) overcome the size and efficiency limitation of the linear supplies. In an SMPS, the utility line voltage AC is rectified to DC using a diode bridge. The rectified voltage is boosted to a high voltage level to provide Power Factor correction and universal operation for varying utility voltages. The boosted common DC voltage is converted to the desired DC voltage levels using DC-to-DC converters, or desired AC voltages using DC-to-AC inverters. The DC-to-DC and DC-to-AC converters or inverter use high frequency switches and transformers. The switching frequencies range from thousands of hertz to hundreds of thousand hertz. So, SMPS uses smaller sized magnetics compared to LPS. However, even these magnetic components are over thirty percent of the overall volume of an SMPS.
The power converter or inverter of the state of the art can be viewed as a composite of many conversion stages. In a LPS Transformer Stage, Rectifier Stage and Output Voltage Regulation stage are generally used. In an SMPS Rectifier Stage, power Factor Correction stage (PFC), DC Boost Stage and DC-to-DC Conversion Stage, and Output Voltage Regulation stage. Additional functions such current Inrush control, soft start, dimming, pre-charge stages are implemented for different applications. The efficiency of a SMPS depends on the conduction and switching losses in its electronic components. Each stage of an advanced SMPS operates near ninety percent efficiency compared to less than eighty percent of the Linear Power Supplies. However, multiple stages employed in SMPS reduce the cumulative efficiency of the overall system. A three stage SMPS with 90% efficiency yields an effective 73.1% efficiency.
Each stage of SMPS power conversion is going through changes for improvements in cost, size and efficiency. To achieve higher efficiencies, methods to reduce the number of conversion stages, methods to replace loss prone elements such as diodes in the conduction path with the semiconductor switches, methods to increase switching frequencies and reduce noise by using monolithic packages have been illustrated. In addition, methods to replace magnetic transformers with piezoelectric transformers and method to eliminate the magnetics for conversion have been illustrated as described herein
The diode used for rectification stage can be replaced with semiconductor switches. U.S. Pat. No. 6,563,726 illustrates a synchronous bridge rectifier for rectifying AC input to DC with low conduction loss. U.S. Pat. No. 5,510,972 illustrates a bridge rectifier with an active switch and control circuits. U.S. Pat. No. 7,408,796 illustrates an integrated synchronous rectifier package.
Combining PFC and DC-to-DC conversion to one stage is being tried. A paper titled, Single Stage Isolated PFC Topologies, by Steven M. Sandler, Charles Hymowitz, Harold Eicher illustrates topologies for single stage PFC and isolation. Single Stage ZVS-PWM Inverter outlined in the paper titled “Commercial Frequency AC to High Frequency AC Converter with Boost-Active Clamp Bridge Single Stage ZVS-PWM Inverter” published in IEEE Transaction on Power Electronics, Volume. 23, No. 1, January 2008, exemplify the attempts to increase efficiency of a high frequency Induction heating element with these techniques.
A paper titled “Power Factor Correction and Efficiency Investigation of AC-DC Converters Using Forced Commutation Techniques” by K. Georgakas, A. Safacas, in IEEE ISIE 2005, Jun. 20-23, 2005, Dubrovnik, Croatia, investigates power factor correction and efficiency using MOSFET bridges and forced commutation techniques.
It is well known in the art of the inrush currents due to link capacitors used to smooth ripple currents and holdup capacitors provide continued service for a short time. To mitigate the inrush current, soft start circuits or inrush control circuits are used. The circuits to control inrush currents are provided at the AC Line inputs or the rectified output sections.
“Investigation of High-density Integrated Solution for AC/DC Conversion of a Distributed Power System” Dissertation submitted by Bing Lu to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering illustrates methods to reduce the hold up capacitor size.
U.S. Pat. No. 5,920,186 illustrates a Triac relay based control circuit for utility AC line before rectification. U.S. Pat. No. 5,903,451 illustrates a variable frequency start up circuit for the rectified line AC voltage. The charging current of the link capacitors is controlled using a switch and a control circuit. U.S. Pat. No. 7,379,311 B2 illustrates inrush current limiting circuits and its control for use in the rectified stage. The current limiting resistors used in these circuits turn on when the inrush conditions due to Power supply start up or changes voltage levels are detected.
U.S. Pat. No. 6,115,267 illustrates an AC-DC power converter with no input rectifiers and no PFC stage and uses switching means connecting the primary winding of the transformer to AC source. Back to back, MOSFET Switches are used in U.S. Pat. No. 6,115,267 so that the output of the push-pull transformer is of the same polarity regardless of the polarity of the instantaneous input. The use of MOSFET also facilitates soft start stage.
The size of the magnetics decreases as the switching frequency increases. Planar transformers are being used to reduce the size and reduce conversion losses. U.S. Pat. No. 5,010,314 illustrates a low profile planar transformer with printed circuit board and magnetic housing for switching frequencies of one mega Hz (1 MHz). U.S. Pat. No. 7,414,510 illustrates methods to reduce the size of planar transformer as compared to the transformer size of U.S. Pat. No. 5,010,314.
Piezoelectric transformers are used to overcome the noises generated by magnetic transformers. U.S. Pat. No. 5,969,954 demonstrates an AC-DC converter with piezoelectric transformer. U.S. Pat. No. 6,738,267 B1 illustrates the design of a Switched Power Converter with a piezoelectric transformer.
The magnetic core can be eliminated with frequencies above 1 MHz. US patent application publication US 2005/0156699 A1 illustrates a coreless PCB transformer signal and energy transfer. U.S. Pat. No. 5,583,421 illustrates a switched mode Single Ended Primary Inductor Converter (SEPIC) to achieve Line isolation with out the use of transformers. U.S. Pat. No. 6,873,139 illustrates generating negative voltages with out using transformers.
A paper titled “A novel AC-DC Converter un-requiring inductors for power conversion” published by Man-Seop Lee; Young-Chang Cho; Hyeong-Woo Cha, Applied Power Electronics Conference and Exposition, 2008, APEC 2008. Twenty-Third Annual IEEE Volume, Issue, 24-28 Feb. 2008 Page(s):1358-1360, demonstrates an SMPS, which does not use inductors and high voltage capacitors for rectification. This design features very low no load power but does not provide galvanic isolation.
The technological advances hereto illustrated are specialized for each individual converter and inverter applications such as AC-to-DC; AC-to-AC, DC-to-AC and DC-to-DC. These prior art supplies used multiple conversion stages. Even with reduced number of power conversion stages in specific applications, prior art converters do not yield high efficiency.
The department of energy states that disruptive power conversion architectures are necessary to meet the cost and efficiency goals to make alternate energy such as solar power commercially feasible. Disruptive power conversion architecture is needed eliminate many different power supplies, by combining many output levels, each consuming power even when they are idle.
The need exists for novel architectures to meet the multi faceted electric conversion needs with improved efficiency, smaller size and lower costs for use in appliances, lighting, electronic equipment, alternate energy generators and electric vehicles. The need exists for bidirectional power converters. Need exists to provide multiple feature such as, programmable output type (AC or DC), output levels, output frequency and duration, in a single converter to reduce the number of converters used. The need exists to provide additional functions, with the same modules used for power conversion, such as but not limited to high voltage pre-charge, dimming, soft start, and current inrush control. The need exists for quick charging and discharging of electric power for Electric Vehicle operation and power holdover functions in the event of power outage. The need exists for compact power converters for portable operations. The need exists to implement power conversion with common semiconductor chips and common modules. The need exists to utilize multiple high efficiency converters in parallel to provide, higher capacity conversion with out affecting overall conversion efficiency.